Question: $ { {4} \times \left[\begin{array}{rrr}{1} & {3} & {1} \\ {2} & {1} & {3}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{4}\times{1} & {4}\times{3} & {4}\times{1} \\ {4}\times{2} & {4}\times{1} & {4}\times{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{4} & {12} & {4} \\ {8} & {4} & {12}\end{array}\right]}$